The present invention relates to a method and an apparatus for manufacturing spokes of a wire material.
Stress-resistant and reliable spokes are an essential feature of high-quality wheels for bicycles. Other than spokes made of spoke wire, some spokes are manufactured of non-metallic materials such as fiber-reinforced plastics. However, metal wire spokes still show many advantages over spokes of other materials, thus offering possibilities of manufacturing light-weight and permanent, durable wheels specifically in the field of sports bicycles.
In the case of metal spokes, the decrease of the spoke wire to different diameters is a particularly significant step, since it allows considerable weight savings. The methods used and the machinery employed are particularly significant since they have a great impact on the durability and stability of the spokes. Thus, e.g. spoke wire drawing as it is described in DE 466 866 is rather disadvantageous to the material structure and thus to its stability under load. Reducing machines which reduce the diameter by hammering have been found to be particularly advantageous. This improves the toughness of the wire material and enhances the stability under load of the spoke.
The machines known in the prior art per se allow reliable manufacturing of spokes where the desired different thicknesses can be adjusted with sufficient precision. However, different wheel types and spoke insertion systems require a great variety of spoke types showing different sections of varying thickness and different lengths of transition sections between the different thickness sections. The known manufacturing machines and manufacturing methods only achieve comparatively rough tolerance ranges so that transition sections may turn out to be longer or shorter in different and in particular even in the same types of spokes. Although these tolerances actually do not affect the technical quality of the spokes they cause optical differences which are undesirable. To prevent these differences in a finished wheel, the spokes may be selected or classified prior to mounting. However, this considerably increases the operating steps and produces more rejects.
It is therefore the object of the present invention to provide an improved manufacturing of spokes, in particular yielding higher precision and narrower tolerances.